There was a lot to digest in the plan itself, as well as some interesting language to decode and interpret in the delivery of the speech. Below are reactions to four key moments in the speech and why they are worth remembering.

In case you missed it, here's a video of the speech:

It is no surprise Obama's plan is being criticized by Republicans, but even among environmentalists and climate hawks the plan has received mixed reviews.

Al Gore called it "a terrific and historic speech, by far the best address on climate by any president ever."

Rolling Stone's Tim Dickinson was also impressed:

i can't really believe we're hearing a president of the united states delivering this speech #longtimecoming

For me personally, yesterday was a weird series of ups and downs. I was excited and encouraged by Obama's pledge to instruct the Environmental Protection Agency to establish new rules for limiting the amount of carbon pollution existing power plants are allowed to release into the atmosphere, but later in the evening I attended a screening of the new Gasland II documentary, which focuses significant time explaining the many unsettling ways EPA regulators consistently fail to protect citizens negatively affected by the natural gas industry. I couldn't help but feel a bit discouraged that even with strong new rules, the EPA may not fulfill the promise of reducing carbon pollution to the extent they could.

I was not the only one left wondering how effective the EPA will be at enforcing these new rules.

Earlier this year, the EPA delayed a rule limiting greenhouse gas emissions from new power plants. The agency will revive the rule in September and will establish separate standards for gas- and coal-fired power plants, as the utility industry had sought, according to people familiar with the agency’s plans who spoke on the condition of anonymity because of the sensitivity of the issue.

You either require some efficiency measures, which is too weak to matter much, or you require carbon capture and sequestration, which is politically untenable, since it would effectively wipe out the U.S. coal fleet (CCS is not financially viable anywhere). There’s no way to reduce carbon from a coal plant a medium amount. Coal just is carbon.

To me this signals that existing-plant standards aren’t going to bite much. I hope I’m wrong.

On the bright side, Greg Sargent found "the most interesting thing about Obama’s big climate change rollout speech is how aggressive and unapologetic a pitch he made for the virtues of government regulation."

Perhaps the most surprising news was that Obama addressed the Keystone XL pipeline. It was expected he would remain silent on the issue, eventually using the new climate action plan as a way to please opponents of KXL in advance of approving the controversial project.

What's confusing, however, is that Obama's statement has been interpreted in different ways, with some concluding it means he intends to reject the pipeline, while others see it as a hint he plans to approve the project.

And then there’s the word “significantly.” What does that mean? To be significant means having a noticeable effect. Now Keystone XL, as designed, would have a daily transport capacity of about 800,000 barrels of oil. Is that significant? It is to you. It’s even significant to the United States, which uses about 20 million barrels per day. But in the scheme of the whole world — and we are talking about GLOBAL warming — it’s not really significant at all.

350.org founder Bill McKibben has been leading a movement pressuring universities and banks to divest from fossil fuel companies as a way to drain the industry of funding and make a statement about the morality of profitting off destruction. I was seriously shocked when I heard Obama make a quick, but powerful reference to this movement in the speech.

Chris Hayes was also surprised:

"Invest, divest" is the most crypto-radical line the President has ever uttered.

"We have a moral obligation to leave our children a planet that’s not polluted or damaged, and by taking an all-of-the-above approach to develop homegrown energy and steady, responsible steps to cut carbon pollution, we can protect our kids’ health and begin to slow the effects of climate change so we leave a cleaner, more stable environment for future generations."

This portion of the plan alone - not to mention anything else problematic found within it, such as endorsement of nuclear energy and illusory "clean coal"/carbon capture and storage (CCS) technology - would prevent the actions outlined in his Fact Sheet from taking place.

In fact, children’s health and air quality nationwide are directly threatened by the promotion of further fracking and natural gas drilling activity. There is a clear disconnect between the president’s stated commitment to a healthy future for children, and the vast expansion of natural gas drilling and fracking, which are scientifically proven to be polluting the air and drinking water of Americans.

"Burning natural gas is about one-half as carbon-intensive as coal, which can make it a critical 'bridge fuel' for many countries as the world transitions to even cleaner sources of energy," reads the plan.

That premise is false. When measured in its entire life cycle - as Cornell University researchers found - fracked gas is actually dirtier than coal and therefore is a bridge to nowhere other than extreme climate disruption. That's due to fugitive methane emissions, conveniently left out of the climate plan: methane is a greenhouse gas far more potent than carbon dioxide.

The President’s Climate Action Plan says methane is 20 times more powerful a greenhouse gas than carbon dioxide. This is incorrect, it’s far more than that – for the first 20 years, methane is 80 to 105 times more powerful, than CO2 as a warming agent in the atmosphere. This means you need between 80 to 100 pounds of CO2 to equal the warming potential of 1 pound of methane. So even limited methane leaks from fracked wells (not to mention compressors and pipelines) can make fracked gas worse for climate than coal. And the leaks aren’t minimal or easily solvable. And methane is leaking like crazy. A series of peer reviewed studies have now put the leakage rates at between seven and 17%. Above one to three percent, the science tells us that developing fracked gas is worse than coal for the atmosphere.

There will surely be more discussion of this new climate change plan in the coming days, weeks and months, so keep an eye on this space for the latest.